You may be able to put some lead in the stock as well. Pull the butt pad off and see what kind of space is available. I've never done this with an 870 like yours. It might be nice to put extra weight in both ends to even out the balance.

If you install a synthetic buttstock there's plenty of room to add so much lead that you won't want to carry it.

You can also drill a hole in the middle of the mag tube cap, then add a bolt to fit into the back of a mercury recoil reducer or a piece of round bar stock that's been drilled and tapped. Or replace the two-shot plug with a piece of steel bar stock that's just under the spring diameter, but slightly bevel the edges to allow the spring coils to slip by.

For bar stock, there are lots of metal jobbers, but some won't want to deal with the public for something that small. See if there is a Metal Supermarket in your city if all else fails.

For a simple fix for the stock I found that you could fill it with shot and then place plumbers putty over it to where it bulged a little and then installed the pad. It was real easy to take out if you wanted to. Jackie B.

Buy a combat seven shot extention tube.Go to hardware store to buy a long bolt and several panel washers to go in tube and locking nuts.You can add or subtract the weight(washers) to your specs.I leave space ,about half inch, so washers can slide during recoil.It does tame the recoil some.

The Remington steel plug will not fit in newer Remington shotguns that have the plastic twist style spring retainer. The guns the steel plug were made for also had a hole in the magazine tube to hold the plug in position. Newer Remington 870s do not have this hole,

Just to play with the weight to reduce recoil procedure, I added one of the old Remington steel plugs to an 870 trap along with filling the wood stock bolt hole with lead shot. I wound up with a 10 pound 870 that does not kick, but is slow to swing.

If I had a newer 870, I would look to adding a steel plug that would be the same length as the factory plug. If you made it the same diameter as the head of the factory plug it would be small enough to fit through the dimples in the magazine tube. I would suggest then using a different magazine spring that you could shorten a little since the factory plug only has about a half inch resting on the plug. Some old timers who used mercury recoil plugs in their magazine tube would have the spring in two parts so you could have part of it before and part after the recoil plug. I have destroyed the old style spring retainer when I had a bolthead resting against it and the rest of the bolt inside the magazine spring.

If your 870 has a syntheic stock, I would use one of the soft Remington recoil pads they sell aftermarket if your stock already does not have one, . Adding a proportinal amount of weight to the stock that you add to the magazine tube will help keep your balance some what closer to the original balance point,

You might also want to consider one of those ported extended choke tubes for when you are shooting 3 1/2 inch loads.

There is an old joke about the Mossberg 3 1/2 inch pump shotguns when they first came out. People would trade them in at gunstores with 2 rounds shot out of a box of 25. The owner fired one. Could not believe it kicked so hard so fired a second one. Then decided that was more than they ever wanted to experience so they traded it in for something else.

For those Remington shotguns using the 1187 style mag tube and mag cap, any steel plug that is larger in diameter than the spring will have to have slots machines on opposite sides of it to slip past the plug dimples in the mag tube. Some late model 1100s use this retention system, as do some late model 870s. Weights that fit inside the spring are small enough in diameter to slip past the dimple.

I don't like much extra weight in the front end of a shotgun. I prefer weight in the stock. I have drilled about a one inch hole from the bottom of the pistol grip about two inches deep and added mallory metal there. Mallory is expensive, but is a lot heavier than lead. Buy it before you drill so you can drill and fit it correctly. A solid brass bar can also be added in the stock, but you should drill and tap a hole in the center so you can tread in a bolt for future removal. I would also add a rubber washer on each end of the brass bar for a snug fit against the recoil pad.